[PATCH] ASoC: nau8822: choose the best master clock prescalar

[David Lin]

On 2022/5/24 下午 04:38, Hui Wang wrote:
>
> On 5/24/22 16:07, David Lin wrote:
>> On 2022/5/24 上午 11:33, Hui Wang wrote:
>>> We have an imx6sx EVB with the codec nau8822, when playing the audio
>>> with 48k sample rate, the audio sounds distorted and obviously faster
>>>
> <snip>
>>> -            div = i;
>>>           }
>>>           dev_dbg(component->dev, "master clock prescaler %x for fs 
>>> %d\n",
>>>               div, rate);
>>
>> Regarding to your environment with input MCLK is 24 MHz, I think you 
>> should enable PLL for the internal process of codec.
>>
>> So you should do the following calls/operations:
>>
> Thanks for your suggestion. In our case, we use the simple-card as the 
> machine driver, the simple-card hard-codes the 2nd parameter of 
> snd_soc_dai_set_sysclk() to 0, and we don't plan to write a new 
> machine driver since sound quality is pretty good if setting to 46875Hz.
>
> So according to your experience, does the new algorithm bring any side 
> effect or break existing platforms? If so, we have to write a new 
> machine driver (that is a big effort).
>
> Thanks,
>
> Hui.
>
Even you can hear better sound quality than original, it don't still 
have better performance(THD+N) than MCLK is 256FS. Generally,  we will 
suggest the below that for customer support.
1. Check dts description from simple-card about the value of mclk-fs is 
256? The reason is nau8822 codec just support 256FS. Besides, the I.MX 
EVB should be with flexible clock generation.
2. Based on the flexible clock generation, you should input 12.288Mhz as 
MCLK, so the simple-card is suitable for your case with low effort.
3. If your MCLK is always 24MHz, PLL enable is preferred as previous 
mention. One is to implement/porting a machine driver, the other is to 
revise asoc_simple_hw_params callback function from simple-card-utils.c.
>> //PLL
>>     ret = snd_soc_dai_set_sysclk(codec_dai, NAU8822_CLK_PLL,
>>                       24000000, SND_SOC_CLOCK_IN);
>>     if (ret < 0 )
>>         dev_err(card->dev, "failed to set codec sysclk: %d\n", ret);
>>
>>     ret = snd_soc_dai_set_pll(codec_dai, 0, 0,
>>                   24000000, 256 * params_rate(params));
>>     if (ret < 0 )
>>
>>         dev_err(card->dev, "failed to set codec pll: %d\n", ret);
>>
>> David
>>